The present invention relates to ophthalmic lenses. More particularly, the invention relates to multifocal ophthalmic lenses for use in or on the eye, such as intraocular lenses, contact lenses, corneal implant lenses and the like.
The general construction of a multifocal ophthalmic lens is known in the art. For example, Portney U.S. Pat. No. 5,225,858, which is incorporated herein by reference, discloses a multifocal ophthalmic lens including a central zone circumscribed by multiple concentric, annular zones. This patent discloses multifocal lenses having good image quality and light intensity for near objects. The multifocal lens of this patent includes zones for near vision correction in which the vision correction power substantially constant throughout.
Although multifocal lenses of this type provide very effective vision correction, further enhancements would be advantageous.
For example, experience with multifocal lenses as described above has identified two general types of night time visual symptoms referred to as xe2x80x9cglare or flarexe2x80x9d and xe2x80x9chalosxe2x80x9d. The xe2x80x9cglare or flarexe2x80x9d symptom manifests itself as radial lines radiating from distant small bright objects at night. The xe2x80x9chalosxe2x80x9d symptom generally manifest itself as diffuse shadows surrounding distant small bright objects, again noticed at night. These visual symptoms are likely caused by out of focus light passing through the near zone or zones of the lenses.
New ophthalmic lenses which address one or more the above-noted symptoms have been discovered. The present lenses take advantage of the discovery that one or more modifications to the surface of a multifocal lens can provide a beneficial reduction in at least the perception of one or more of the above-noted night time visual symptoms. These modifications can be very conveniently and effectively implemented substantially without increasing the cost or difficulty of manufacturing such lenses. The present lenses preferably reduce the size of the major halo which may be apparent when viewing distant objects at night time. In addition, the central zone of the present lenses preferably is modified to change the vision correction power above the baseline diopter power toward the center of the lens to provide an increase in ray density which enhances near image performance. In summary, the present modification or modifications to the multifocal lenses provide additional advantages in already effective multifocal ophthalmic lenses.
In one broad aspect of the present invention, an ophthalmical lens having a baseline diopter power for far vision correction is provided. The ophthalmic lens comprises a near zone, preferably an annular near zone, including an inner region, having a substantially constant vision correction power greater than the baseline diopter power and having vision correction powers greater than the baseline diopter power which reduce the size, that is the apparent or perceived size, of a halo caused by passing light to the near zone relative to the halo caused by passing light to a similar near zone of a substantially identical lens in which the similar near power has a constant vision correction power throughout.
Preferably, the near zone has a highest vision correction power, which may be the substantially constant vision correction power of the inner region, and includes an outer region located outwardly of the inner region. This outer region has vision correction powers which are progressively reduced from the highest vision correction power of the near zone to a reduced near vision correction power which is between about 50% and about 85% of the highest vision correction power of the near zone. The inner region has an innermost end and the outer region has an outermost end. The radial width of the inner region more preferably is in the range of about 30% to about 85% of the radial distance between the innermost end of the inner region and the outermost end of the outer region.
Without wishing to limit the invention to any particular theory of operation, it is believed that the reduction of the vision correction power in the outer region of the near zone is effective to reduce the size of the most apparent or most perceived halo around small light sources viewed from a distance, for example, at night time.
In one very useful embodiment, the present ophthalmic lenses further comprise an additional near zone, preferably an annular additional near zone, located outwardly of, and preferably circumscribing, the near zone and having vision correction powers greater than the baseline diopter power. The additional near zone preferably includes vision correction powers which diffuse, or increase the apparent or perceived size of, a halo caused by passing light to the additional near zone relative to the halo caused by passing light to a similar additional near zone of a substantially identical lens in which the similar additional near zone has a constant vision correction power throughout.
In one very useful embodiment, the width of the additional near zone is less than about 40% of the radial width of the near zone. The additional near zone has an inner end and an outer end and vision correction powers which preferably increase progressively from the inner end to the outer end.
The present ophthalmic lenses preferably reduce the size of the halo resulting from passing light to the near zone and increase the size of the halo resulting from passing light to the additional near zone. The overall effect of the near zone, and preferably the additional near zone, of the present ophthalmic lenses preferably is to effectively and advantageously reduce the apparent or perceived xe2x80x9chaloxe2x80x9d visual symptom, and more preferably the xe2x80x9cglare or flarexe2x80x9d visual symptom, which have been noted during use of previous multifocal lenses.
The present ophthalmic lenses preferably are selected from intraocular lenses, contact lenses, corneal implant lenses and the like.
The present ophthalmic lenses may, and preferably do, include a central zone having a vision correction power greater than the baseline diopter power. The near zone is located outwardly of, and preferably circumscribes, the central zone.
In an additional broad aspect of the present invention, ophthalmic lenses having a baseline diopter power for far vision correction are provided which comprise a central zone including a center region, an intermediate region, and an outer region. The center region has a vision correction power, for example, substantially equal to the baseline diopter power, although the center region can have a vision correction power which is less than or greater than the baseline diopter power. The intermediate region is located outwardly of the center region and has a vision correction power which is the highest vision correction power in the central zone. The outer region is located outwardly of the intermediate region and has a vision correction power equal to the vision correction power of the center region. The highest vision correction power in the central zone is closer, in terms of radial distance, to the vision correction power of the center region than to the vision correction power of the outer region equal to the vision correction power of the center region.
Without wishing to limit the invention to any particular theory of operation, it is believed that the modification in which the highest vision correction power of the central zone is closer to the vision correction power of the center region increases the ray density closer to the center or optical axis of the lens, which enhances near image performance.
The vision correction powers of the central zone preferably vary progressively. The highest vision correction power in the central zone preferably is located about 40% or less, more preferably about 35% or less, of the distance, for example, the radial distance, between the vision correction power of the center region and the vision correction of the outer region equal to the vision correction power of the center region.
In one very useful embodiment, the ophthalmic lenses preferably further comprise a first outer zone located outwardly of the central zone and having a vision correction power less than the baseline diopter power; and a second outer zone located outwardly of the first outer zone and having a vision correction power greater than the baseline diopter power. Preferably, the intermediate region, the outer region, the first outer zone and the second outer zone are annular and circumscribe the center region, the intermediate region, the outer region and the first outer zone, respectively.
The second outer zone preferably includes vision correction powers which reduce the size of a halo caused by passing light to the second outer zone relative to the halo caused by passing light to a similar second outer zone of a substantially identical lens in which the similar second outer zone has a constant vision correction power throughout. The second outer zone preferably has inner and outer regions and other characteristics similar to those of the near zone described elsewhere herein.
The present ophthalmic lenses preferably include a third outer zone located outwardly of the second outer zone and having a vision correction power greater than the baseline diopter power. This third outer zone preferably includes vision correction powers which diffuse a halo caused by passing light through the third outer zone relative to the halo caused by passing light to a similar third outer zone of a substantially identical lens in which the similar third outer zone has a width which preferably is less than about 40% of the width of the second outer zone. The third outer zone preferably has an inner end and an outer end and vision correction powers which increase progressively from the inner end to the outer end.
In a very useful embodiment, the ophthalmic lenses of the present invention further comprise a fourth outer zone located outwardly of the second outer zone and inwardly of the third outer zone and having vision correction powers less than the baseline diopter power. This fourth outer zone preferably has an inner region having a vision correction power, an intermediate region located outwardly of the inner region and an outer region located outwardly of the intermediate region. The intermediate region has a vision correction power which is increased relative to the vision correction power of the inner region and is the highest vision correction power in the intermediate zone and an outermost diopter power equal to the vision correction power of the inner region. The outer region has a vision correction power which is the lowest vision correction power of the fourth outer zone. The highest vision correction power of the fourth outer zone is located closer, that is radially closer, to the vision correction power of the inner region than to the outermost vision correction power of the intermediate region. This preferred fourth outer zone configuration provides the present lenses with enhanced far vision performance, particularly in dim light and/or at night time.
The first, second and third outer zones preferably are annular and the first annular zone circumscribes the central zone, the second outer zone circumscribes the first outer zone and the third outer zone circumscribes the second outer zone. In the event the fourth outer zone is included, the fourth outer zone preferably is annular and circumscribes the second outer zone and is circumscribed by the third outer zone.
The portions of the present lenses between the various zones of differing vision correction powers can be referred to as transition portions or zones. Such transition portions or zones can provide for an abrupt or xe2x80x9cstep functionxe2x80x9d change in vision correction power. Preferably, however, the transition portions or zones provide for a more gradual or progressive change in vision correction power.
The desired powers for the present lenses can be provided in various different ways, including the use of refracting surfaces. In one preferred embodiment, the lens has anterior and posterior surfaces, at least one of which is shaped to provide the desired vision correction powers. With this construction, the progressive portion or portions of the lens are aspheric, and although the regions of the lens of constant power can be spheric if desired, preferably they are also aspheric. In a preferred construction, the lenses of the invention are aspheric throughout the annular zones and the central zone, and this provides certain advantages in designing the lens and also can be used to compensate for spherical aberrations for far vision portions and near vision portions of the lens.
For a contact lens, it is preferred to shape the posterior surface to fit the curvature of the patient""s eye and to configure the anterior surface to provide the desired correction.
Each and every feature described herein, and each and every combination of two or more of such features are included with the scope of the present invention provided that the features included in any such combination are not mutually inconsistent.
These and other aspects of the present invention are apparent in the following detailed description and claims particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.